The present invention relates generally to the utilization of lignocellulosic biomass, and in certain embodiments to processes that involve processing biomass that has been subject to liquefaction to recover heat therefrom, and the integration of such processing into the manufacture of useful products such as ethanol.
As further background, in the conversion of biomass to products of commerce, it is desired that the costs and equipment associated with the physical and chemical treatments of the biomass be minimized. Downstream products of biomass are often commoditized from other sources, and thus biomass-based manufacturing costs must be held tightly in check.
One challenge that is presented in biomass processing is the difficulty in moving the biomass to, within and through equipment needed to physically and/or chemically treat the biomass. Processing at low biomass solids content enhances flowability and transport in some cases, but minimizes productivity for the downstream product, often fatal to the commercial viability of the process. Processing at high biomass solids enhances productivity, but the attendant thick, wet mass is difficult to move, consumes high levels of energy for transport, and/or cannot effectively be processed through heat recovery equipment such as heat exchangers due to an in ability to pump the mixture and/or plugging of the heat exchangers. The effective recovery and recycle of energy used in processing of the biomass can also be vital to commercial viability.
In one field of interest, fuel ethanol has been produced by fermentation of biomass feedstocks derived from plants. Currently, fuel ethanol is commercially produced from feedstocks of cornstarch, sugar cane and sugar beets. These materials, however, find significant competing uses in the food industry, and their expanded use to make fuel ethanol is met with increased prices and disruption of other industries. Alternative fermentation feedstocks and technologies for their utilization are thus highly sought after.
Lignocellulosic biomass feedstocks are available in large quantities and are relatively inexpensive. Such feedstocks are available in the form of agricultural wastes such as corn stover, corn fiber, wheat straw, barley straw, oat straw, oat hulls, canola straw, soybean stover, grasses such as switch grass, miscanthus, cord grass, and reed canary grass, forestry wastes such as wood, e.g. aspen wood and sawdust, and sugar processing residues such as bagasse and beet pulp. Cellulose from these feedstocks is converted to sugars, which are then fermented to produce the ethanol.
A difficulty in using lignocellulosic feedstocks is that the useful sugar content of the biomass is largely caught up in natural polymers such as cellulose and hemicellulose, and conditions or agents must be used to convert those polymeric substances to simple sugars. For this reason, research has focused upon methods for processing lignocellulosic biomass to create process feeds containing simple sugars. For such methods to succeed, high starting biomass solids levels and effective digestion of the biomass are important to providing a fermentable medium with high enough sugar levels to make for viable fermentations. However, such high solids levels present many difficulties in manufacturing, as discussed above.
Despite previous efforts relating to processing lignocellulosic biomass feedstocks and their ultimate use in the production of ethanol and other products, needs remain for improved and alternative biomass utilization processes, including in the production of ethanol or other useful substances from fermentation. In certain of its aspects, the present invention is addressed to these needs.